In typical cellular wireless communication systems, wireless communication devices (WCDs) (e.g., cell phones, personal digital assistants, laptops, netbooks, tablets, and/or other wirelessly equipped devices) subscribe to service from a given cellular wireless service provider. In practice, a service provider will operate one or more networks (sometimes referred to as radio access networks (RANs)) including base transceiver stations (BTSs) that radiate to define wireless coverage areas where the subscriber WCDs can operate.
Through each BTS (and corresponding RAN), a WCD can obtain connectivity to other networks such as the public switched telephone network (PTSN) and the Internet. Further, each RAN may include one or more radio network controllers (RNCs) or the like, which may be integrated with or otherwise in communication with the BTSs, and which may include or be in communication with a switch or gateway that provides connectivity with one or more transport networks. Conveniently with this arrangement, a WCD that is positioned within coverage of the RAN can then communicate with a BTS and in turn, via the BTS, with other served WCDs or with other entities on the transport network.
When a subscriber WCD enters into a coverage area of its service provider, the subscriber WCD may register with the service provider (through a BTS, for instance) and may then engage in wireless communication service via the service provider's network.
Generally, a BTS serving a particular coverage area will operate on a given carrier frequency, or more particularly a given band of frequencies (also referred to as a channel), and communicate with WCDs being served in the particular coverage area on the channel. By way of example, a channel can be defined as a specific frequency block, such as a 1.25 MHz block or a 5 MHz block in a profile frequency band used by the wireless service provider, such as 800 MHz (cellular band), 1.9 GHz (PCS band), or 2.5 GHz (BRS/EBS band). For instance, if a wireless service provider operates in the 800 MHz cellular band, coverage areas of the wireless service provider's RAN will typically operate with channels defined near 800 MHz. And if a wireless service provider operates in the 1.9 GHz band, coverage areas of the wireless service provider's RAN will typically operate with channels defined near 1.9 GHz. In practice, each channel may actually be defined as one frequency block for “forward link” communications from the RAN to WCDs and a corresponding but separate frequency block for “reverse link” communications from WCDs to the RAN.
In a coverage area where wireless communication traffic is particularly high, a BTS serving that coverage area may operate on more than one channel for communicating with the WCDs in that coverage area. The number of channels employed in a given coverage area may depend on various factors, such as the volume of communication traffic expected. For example, in a congested urban location, coverage areas might be designed to employ two or more channels, whereas in a sparsely populated rural location, coverage areas might employ only one channel.
In practice, a RAN may broadcast in each coverage area at least one channel list message (CLM) that specifies channels available for use in the coverage area, so that WCDs in the coverage area can determine which channel to use. If multiple channels are listed, then each WCD receiving the CLM may execute a hashing algorithm to determine which channel to register on in the coverage area. The process of determining a particular channel to use based on a hashing algorithm is referred to as “hashing,” and the particular channel that is determined based on the hashing is referred to as the “hashed channel.” If a WCD is under the coverage of two or more neighboring coverage areas, the WCD may receive a respective CLM from each coverage area.